The present invention relates to improved circuits for sensing conditions related to a processor. In particular, the present invention relates to improvements including sensing whether a processor is installed in a circuit and sensing processor supply voltages.
As processor packaging formats become larger and more complex, containing larger memory caches and being serviced by high speed high capacity busses, problems arise related to determining whether the processor is installed, and whether voltage may be applied, and, once applied, determining how best to regulate the voltage.
In prior art processors, a loop circuit may be used to detect power enable and, by derivation whether the processor is installed and fully seated. Because of the possibility of part damage due to currents from improperly seated parts and resulting poor electrical connections, it is crucial not to apply power unless a processor is fully installed. Such currents may cause the processor itself, the package contacts, and the cartridge to be damaged. Loop circuits have been used, as noted, to derive whether the processor is seated electrically based on the power enable signal as described. Such a derived approach has disadvantages in that the signal must be present for the system to power up. This signal is inappropriate to use as an indicator of a processor or terminator card being installed.
Another factor affecting processor operation is voltage regulation. A typical VRM associated with a processor circuit board has sense lines which allow for better regulation of supplied voltages by providing references to supplied voltages. Problems arise in that sense lines for regulating voltages on a typical circuit board to which a processor may be coupled may be connected to a voltage supply plane in close proximity to the VRM. Sensing voltages at the voltage supply plane of the circuit board may not accurately reflect the true state of voltages which most affect processor operation at a point which most accurately characterizes the voltage levels as they are seen by the processor. Further, voltage drops from circuits within the processor where the supply voltages are used to voltage supply planes where voltage levels are sensed may result in poor or inadequate voltage regulation where it is needed the most, e.g. to regulate voltage supply planes used in the processor.
It would be desirable therefore for an apparatus and method for providing an indication that a processor is properly seated and ready for the application of voltage. It would further be desirable for an apparatus and method which provides for improved regulation for internal processor voltages.
The present invention overcomes the above identified problems as well as other shortcomings and deficiencies of existing technologies by providing a signal to indicate whether the processor is installed. A contact, selected and isolated from an array of contacts used to provide a ground connection for the processor is coupled with circuit for generating a corresponding INSTALL signal indicating whether a processor is installed. The circuit of the present invention allows the difference between the is installation of a processor and the installation of a socket terminator or power-enable card to be detected. One or more contacts forming a portion of the ground plane or grid of a circuit board may be isolated from an existing plurality of contacts in the ground plane. A pull up resistor may be coupled to a supply voltage and the isolated contact and a capacitor may be coupled between the isolated contact and ground plane and a signal line may be coupled to the common node between the resistor, the capacitor, and the isolated contact such that when the processor plugged in, a circuit is completed through the processor between the ground plane and the isolated contact and thus the signal line. The signal is pulled low to ground when the processor is plugged in and is pulled high when the processor is not plugged in, thus providing a direct signal indication of the presence or absence of the processor. It is to be noted that the present invention can be practiced without adversely affecting ground sourcing capacity considerations for the processor.
To further address the shortcomings of the prior art, a circuit board accommodating a processor in accordance with the present invention may include a Voltage Regulation Module (VRM) having voltage sense lines. Voltage may be sensed directly from processor contacts in contrast to sensing voltages at respective power planes or grids within the circuit board leading to improved regulation particularly as processor demands change during operation. One or more voltage sense contacts may be isolated from an existing plurality of voltage supply contacts coupled to the supply plane or grid of a respective supply voltage within the circuit board without adversely affecting power supply current capacity considerations. For example, a contact from the cache voltage supply may be isolated for sensing the cache voltage directly at the processor when plugged in. Core voltage may also be measured in a similar manner by isolating a contact associated with the core voltage supply for sensing the core voltage directly at the processor.